[LeetCode] Binary Tree Level Order Traversal II

Binary
Tree Level Order Traversal II:

Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left
to right, level by level from leaf to root).

For example:

Given binary tree

{3,9,20,#,#,15,7}

,

3
/ \
9  20
/  \
15   7

return its bottom-up level order traversal as:

[
[15,7]
[9,20],
[3],
]

跟前面那个没什么区别，你要顺序添加了做一个reverse也行。

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<vector<int> > levelOrderBottom(TreeNode *root) {
// Start typing your C/C++ solution below
// DO NOT write int main() function

if ( !root )
return vector<vector<int> >();

deque<vector<int> > ans;
vector<int> level;
queue<TreeNode* > Q;
Q.push(root);
int lsum=1;
while(lsum)
{
level.clear();
int next=0;
while(lsum--)
{
TreeNode* t=Q.front();
Q.pop();
level.push_back(t->val);
if ( t->left )
{
Q.push(t->left);
next++;
}
if ( t->right)
{
Q.push(t->right);
next++;
}
}
ans.push_front(level);
lsum=next;
}
return vector<vector<int> >(ans.begin(),ans.end());
}
};